Vapor deposition apparatus and process for continuous indirect deposition of a thin film layer on a substrate

ABSTRACT

An apparatus and related process are provided for vapor deposition of a sublimated source material as a thin film on a photovoltaic (PV) module substrate. A deposition head is configured for sublimating a source material supplied thereto. The sublimated source material condenses onto a transport conveyor disposed below the deposition head. A substrate conveyor is disposed below the transport conveyor and conveys substrates in a conveyance path through the apparatus such that an upper surface of the substrates is opposite from and spaced below a lower leg of the transport conveyor. A heat source is configured adjacent the lower leg of the transport conveyor. The source material plated onto the transport conveyor is sublimated along the lower leg and condenses onto to the upper surface of substrates conveyed by the substrate conveyor.

FIELD OF THE INVENTION

The subject matter disclosed herein relates generally to the field ofthin film deposition processes wherein a thin film layer, such as asemiconductor material layer, is deposited on a substrate. Moreparticularly, the subject matter is related to a vapor depositionapparatus and associated process for depositing a thin film layer of aphoto-reactive material on a glass substrate in the formation ofphotovoltaic (PV) modules.

BACKGROUND OF THE INVENTION

Thin film photovoltaic (PV) modules (also referred to as “solar panels”)based on cadmium telluride (CdTe) paired with cadmium sulfide (CdS) asthe photo-reactive components are gaining wide acceptance and interestin the industry. CdTe is a semiconductor material having characteristicsparticularly suited for conversion of solar energy (sunlight) toelectricity. For example, CdTe has an energy bandgap of 1.45 eV, whichenables it to convert more energy from the solar spectrum as compared tolower bandgap (1.1 eV) semiconductor materials historically used insolar cell applications. Also, CdTe converts more efficiently in loweror diffuse light conditions as compared to the lower bandgap materialsand, thus, has a longer effective conversion time over the course of aday or in low-light (i.e., cloudy) conditions as compared to otherconventional materials.

Solar energy systems using CdTe PV modules are generally recognized asthe most cost efficient of the commercially available systems in termsof cost per watt of power generated. However, the advantages of CdTe notwithstanding, sustainable commercial exploitation and acceptance ofsolar power as a supplemental or primary source of industrial orresidential power depends on the ability to produce efficient PV moduleson a large scale and in a cost effective manner.

Certain factors greatly affect the efficiency of CdTe PV modules interms of cost and power generation capacity. For example, CdTe isrelatively expensive and, thus, efficient utilization (i.e., minimalwaste) of the material is a primary cost factor. In addition, the energyconversion efficiency of the module is a factor of certaincharacteristics of the deposited CdTe film layer. Non-uniformity ordefects in the film layer can significantly decrease the output of themodule, thereby adding to the cost per unit of power. Also, the abilityto process relatively large substrates on an economically sensiblecommercial scale is a crucial consideration.

CSS (Close Space Sublimation) is a known commercial vapor depositionprocess for production of CdTe modules. Reference is made, for example,to U.S. Pat. No. 6,444,043 and U.S. Pat. No. 6,423,565. Within the vapordeposition chamber in a CSS system, the substrate is brought to anopposed position at a relatively small distance (i.e., about 2-3 mm)opposite to a CdTe source. The CdTe material sublimes and deposits ontothe surface of the substrate. In the CSS system of U.S. Pat. No.6,444,043 cited above, the CdTe material is in granular form and is heldin a heated receptacle within the vapor deposition chamber. Thesublimated material moves through holes in a cover placed over thereceptacle and deposits onto the stationary glass surface, which is heldat the smallest possible distance (1-2 mm) above the cover frame. Thecover is heated to a temperature greater than the receptacle.

While there are advantages to the CSS process, the related system isinherently a batch process wherein the glass substrate is indexed into avapor deposition chamber, held in the chamber for a finite period oftime in which the film layer is formed, and subsequently indexed out ofthe chamber. The system is more suited for batch processing ofrelatively small surface area substrates. The process must beperiodically interrupted in order to replenish the CdTe source, which isdetrimental to a large scale production process. In addition, thedeposition process cannot readily be stopped and restarted in acontrolled manner, resulting in significant non-utilization (i.e.,waste) of the CdTe material during the indexing of the substrates intoand out of the chamber, and during any steps needed to position thesubstrate within the chamber.

Accordingly, there exists an ongoing need in the industry for animproved vapor deposition apparatus and process for economicallyfeasible large scale production of efficient PV modules, particularlyCdTe modules.

BRIEF DESCRIPTION OF THE INVENTION

Aspects and advantages of the invention will be set forth in part in thefollowing description, or may be obvious from the description, or may belearned through practice of the invention.

In accordance with an embodiment of the invention, an apparatus isprovided for indirect vapor deposition of a sublimated source material,such as CdTe, as a thin film on a photovoltaic (PV) module substrate.The deposition process is “indirect” in that the sublimated sourcematerial does not plate directly onto the substrate, but is caused tofirst plate onto a transfer device. The transfer device is then moved toa location opposite to the substrate wherein the plated source materialon the transfer device is subsequently sublimated and caused to transferonto a surface of the substrate. Although the invention is not limitedto any particular film thickness, a “thin” film layer is generallyrecognized in the art as less than 10 microns (μm).

The apparatus includes a deposition head configured for sublimating asource material supplied thereto. The transfer device is disposedrelative to the deposition head so that the sublimated source materialplates onto the device. In a particular embodiment, the transfer deviceis configured as a transport conveyor disposed below the deposition headand that moves in an endless loop between an upper leg and a lower leg.The transport conveyor includes an upper surface onto which thesublimated source material plates as the transport conveyor moves in theupper leg. A substrate conveyor is disposed below the transport conveyorand is configured to convey substrates in a conveyance path through theapparatus such that an upper surface of the substrates is opposite fromand spaced below the lower leg of the transport conveyor. A heat sourceis configured at an effective location adjacent the lower leg of thetransport conveyor to cause the source material that plated onto thetransport conveyor along the upper leg to sublimate along the lower leg.The sublimated source material transfers to the upper surface ofsubstrates conveyed by the substrate conveyor.

Variations and modifications to the embodiment of the vapor depositionapparatus discussed above are within the scope and spirit of theinvention and may be further described herein.

In still another aspect, the invention encompasses a process forindirect vapor deposition of a sublimated source material, such as CdTe,as a thin film on a photovoltaic (PV) module substrate. The processincludes sublimating source material in a deposition head, which platesonto a transfer device that is disposed relative to the deposition headfor this purpose. Although not limited to this, the transfer device maybe a first (“transport”) conveyor that moves to a position adjacent to asecond (“substrate”) conveyor, which carries a substrate thereon. Thesource material on the first conveyor is then sublimated and transfers(plates) to an upper surface of the substrate carried by the secondconveyor.

Variations and modifications to the embodiment of the vapor depositionprocess discussed above are within the scope and spirit of the inventionand may be further described herein.

These and other features, aspects, and advantages of the presentinvention will become better understood with reference to the followingdescription and appended claims, or may be obvious from the descriptionor claims, or may be learned through practice of the invention.

BRIEF DESCRIPTION OF THE DRAWING

A full and enabling disclosure of the present invention, including thebest mode thereof, is set forth in the specification, which makesreference to the appended drawings, in which:

FIG. 1 is a plan view of a system that may incorporate embodiments of avapor deposition apparatus of the present invention;

FIG. 2 is a cross-sectional and partial plan view of an embodiment of avapor deposition apparatus according to aspects of the invention;

FIG. 3 is a cross-sectional and perspective view of an embodiment of adeposition head;

FIG. 4 is a cross-sectional view of an alternative embodiment of a vapordeposition apparatus;

FIG. 5 is perspective view of an embodiment of an upper conveyorassembly that may be used in a vapor deposition apparatus in accordancewith aspects of the invention;

FIG. 6 is a perspective view of an embodiment of a conveyor assembly;and,

FIG. 7 is a side view of the conveyor assembly of FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

Reference now will be made in detail to embodiments of the invention,one or more examples of which are illustrated in the drawings. Eachexample is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that various modifications and variations can be madein the present invention without departing from the scope or spirit ofthe invention. For instance, features illustrated or described as partof one embodiment, can be used with another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventionencompass such modifications and variations as come within the scope ofthe appended claims and their equivalents.

FIG. 1 illustrates an embodiment of a system 10 that may incorporate avapor deposition apparatus 100 (FIGS. 2 through 4) in accordance withembodiments of the invention configured for deposition of a thin filmlayer on a photovoltaic (PV) module substrate 14 (referred to hereafteras a “substrate”). The thin film may be, for example, a film layer ofcadmium telluride (CdTe). As mentioned, it is generally recognized inthe art that a “thin” film layer on a PV module substrate is generallyless than about 10 microns (μm), although the invention is not limitedto any particular thickness. It should be appreciated that the presentvapor deposition apparatus 100 is not limited to use in the system 10illustrated in FIG. 1, but may be incorporated into any suitableprocessing line configured for vapor deposition of a thin film layeronto a PV module substrate 14.

For reference and an understanding of an environment in which the vapordeposition apparatus 100 may be used, the system 10 of FIG. 1 isdescribed below, followed by a detailed description of the apparatus100.

Referring to FIG. 1, the exemplary system 10 includes a vacuum chamber12 defined by a plurality of interconnected modules, including aplurality of heater modules 16 that define a pre-heat section of thevacuum chamber 12 through which the substrates 14 are conveyed andheated to a desired temperature before being conveyed into the vapordeposition apparatus 100. Each of the modules 16 may include a pluralityof independently controlled heaters 18, with the heaters defining aplurality of different heat zones. A particular heat zone may includemore than one heater 18.

The vacuum chamber 12 also includes a plurality of interconnectedcool-down modules 20 downstream of the vapor deposition apparatus 100.The cool-down modules 20 define a cool-down section within the vacuumchamber 12 through which the substrates 14 having the thin film ofsublimated source material deposited thereon are conveyed and cooled ata controlled cool-down rate prior to the substrates 14 being removedfrom the system 10. Each of the modules 20 may include a forced coolingsystem wherein a cooling medium, such as chilled water, refrigerant,gas, or other medium, is pumped through cooling coils (not illustrated)configured with the modules 20.

In the illustrated embodiment of system 10, at least one post-heatmodule 22 is located immediately downstream of the vapor depositionapparatus 100 and upstream of the cool-down modules 20 in a conveyancedirection of the substrates. As the leading section of a substrate 14 isconveyed out of the vapor deposition apparatus 100, it moves into thepost-heat module 22, which maintains the temperature of the substrate 14at essentially the same temperature as the trailing portion of thesubstrate still within the vapor deposition apparatus 100. In this way,the leading section of the substrate 14 is not allowed to cool while thetrailing section is still within the vapor deposition apparatus 100. Ifthe leading section of a substrate 14 were allowed to cool as it exitedthe apparatus 100, a non-uniform temperature profile would be generatedlongitudinally along the substrate 14. This condition could result inbreaking, cracking, or warping of the substrate from thermal stress.

As diagrammatically illustrated in FIG. 1, a feed device 24 isconfigured with the vapor deposition apparatus 100 to supply sourcematerial, such as granular CdTe. The feed device 24 may take on variousconfigurations within the scope and spirit of the invention, andfunctions to supply the source material without interrupting thecontinuous vapor deposition process within the apparatus 100 orconveyance of the substrates 14 through the apparatus 100.

Still referring to FIG. 1, the individual substrates 14 are initiallyplaced onto a load conveyor 26, and are subsequently moved into an entryvacuum lock station that includes a load module 28 and a buffer module30. A “rough” (i.e., initial) vacuum pump 32 is configured with the loadmodule 28 to drawn an initial vacuum, and a “high” or “fine” vacuum pump38 is configured with the buffer module 30 to increase the vacuum in thebuffer module 30 to essentially the vacuum pressure within the vacuumchamber 12. Valves 34 (e.g., gate-type slit valves or rotary-typeflapper valves) are operably disposed between the load conveyor 26 andthe load module 28, between the load module 28 and the buffer module 30,and between the buffer module 30 and the vacuum chamber 12. These valves34 are sequentially actuated by a motor or other type of actuatingmechanism 36 in order to introduce the substrates 14 into the vacuumchamber 12 in a step-wise manner without affecting the vacuum within thechamber 12.

In operation of the system 10, an operational vacuum is maintained inthe vacuum chamber 12 by way of any combination of rough and/or highvacuum pumps 40. In order to introduce a substrate 14 into the vacuumchamber 12, the load module 28 and buffer module 30 are initially vented(with the valve 34 between the two modules in the open position). Thevalve 34 between the buffer module 30 and the first heater module 16 isclosed. The valve 34 between the load module 28 and load conveyor 26 isopened and a substrate 14 is moved into the load module 28. At thispoint, the first valve 34 is shut and the rough vacuum pump 32 thendraws an initial vacuum in the load module 28 and buffer module 30. Thesubstrate 14 is then conveyed into the buffer module 30, and the valve34 between the load module 28 and buffer module 30 is closed. The highvacuum pump 38 then increases the vacuum in the buffer module 30 toapproximately the same vacuum in the vacuum chamber 12. At this point,the valve 34 between the buffer module 30 and vacuum chamber 12 isopened and the substrate 14 is conveyed into the first heater module 16.

An exit vacuum lock station is configured downstream of the lastcool-down module 20, and operates essentially in reverse of the entryvacuum lock station described above. For example, the exit vacuum lockstation may include an exit buffer module 42 and a downstream exit lockmodule 44. Sequentially operated valves 34 are disposed between thebuffer module 42 and the last one of the cool-down modules 20, betweenthe buffer module 42 and the exit lock module 44, and between the exitlock module 44 and an exit conveyor 46. A high vacuum pump 38 isconfigured with the exit buffer module 42, and a rough vacuum pump 32 isconfigured with the exit lock module 44. The pumps 32, 38 and valves 34are sequentially operated to move the substrates 14 out of the vacuumchamber 12 in a step-wise fashion without loss of vacuum conditionwithin the vacuum chamber 12.

System 10 also includes a conveyor system configured to move thesubstrates 14 into, through, and out of the vacuum chamber 12. In theillustrated embodiment, this conveyor system includes a plurality ofindividually controlled conveyors 48, with each of the various modulesincluding a respective one of the conveyors 48. It should be appreciatedthat the type or configuration of the conveyors 48 may vary. In theillustrated embodiment, the conveyors 48 are roller conveyors havingrotatably driven rollers that are controlled so as to achieve a desiredconveyance rate of the substrates 14 through the respective module andthe system 10 overall.

As described, each of the various modules and respective conveyors inthe system 10 are independently controlled to perform a particularfunction. For such control, each of the individual modules may have anassociated independent controller 50 configured therewith to control theindividual functions of the respective module. The plurality ofcontrollers 50 may, in turn, be in communication with a central systemcontroller 52, as diagrammatically illustrated in FIG. 1. The centralsystem controller 52 can monitor and control (via the independentcontrollers 50) the functions of any one of the modules so as to achievean overall desired heat-up rate, deposition rate, cool-down rate,conveyance rate, and so forth, in processing of the substrates 14through the system 10.

Referring to FIG. 1, for independent control of the individualrespective conveyors 48, each of the modules may include any manner ofactive or passive sensors 54 that detect the presence of the substrates14 as they are conveyed through the module. The sensors 54 are incommunication with the respective module controller 50, which is in turnin communication with the central controller 52. In this manner, theindividual respective conveyor 48 may be controlled to ensure that aproper spacing between the substrates 14 is maintained and that thesubstrates 14 are conveyed at the desired conveyance rate through thevacuum chamber 12.

FIGS. 2 through 7 relate to aspects of particular embodiments of a vapordeposition apparatus 100 in accordance with aspects of the invention.Referring to FIG. 2, the apparatus 100 includes a deposition head 110that is configured for sublimating a source material, such as CdTe,supplied thereto. The deposition head 110 is depicted schematically inFIG. 2, and it should be understood that the apparatus is not limited toany particular configuration of deposition head 110 or depositionprocess. A particular embodiment of a deposition head 110 is illustratedin FIG. 3 and described in greater detail below. A transfer device isdisposed below the deposition head 110 and provides a surface onto whichthe sublimated source material plates. The transfer device then moves toa position wherein the source material plated thereon is re-sublimatedand plates onto a substrate 14. The transfer device may take on variousconfigurations within the scope and spirit of the invention, and may beany device or mechanism that is suitable for transferring sublimatedsource material to a substrate in an indirect deposition process, asdescribed herein.

In a particular embodiment described herein, the transfer device isconfigured as a conveyor 160 that moves in an endless loop aroundsprockets 238 (with at least one sprocket 238 being a drive sprocket)between an upper leg 162 and a lower leg 164. The upper leg 162 is thehorizontal portion of the conveyor 160 opposite from the deposition head110. As the conveyor 160 moves along the upper leg 162, sublimatedsource material from the deposition head 110 condenses (plates) onto theupper surface 163 of the conveyor 160. As the conveyor 160 continues inits endless loop path, the upper surface 163 (with source materialplated thereon) moves along the lower leg 164, as indicated by thearrows in FIG. 2. The lower leg 164 is the horizontal portion of theendless loop path that is moving in the opposite direction from thehorizontal upper leg 162.

A substrate conveyor 166 is disposed below the transport conveyor 160,in particular below the lower leg 164. The substrate conveyor 166 isconfigured to convey substrates 14 in a conveyance path through thevapor deposition apparatus 100 such that an upper surface of thesubstrates 14 is opposite from and spaced below the lower leg 164 of thetransport conveyor 160. The distance between the upper surface of thesubstrate 14 and the surface 163 of the conveyor 160 is referred to as adiffusion length, and is the distance sublimated source material (fromthe surface 163) must travel prior to condensing onto the upper surfaceof the substrate 14. The substrate conveyor 166 moves the substrates 14along a conveyance path that ensures a uniform, constant diffusionlength through the apparatus 100.

The transport conveyor 160 and substrate conveyor 166 may be configuredwithin any manner of housing structure 186, with the deposition head 110configured above the housing structure 186.

To maintain a precise horizontal aspect of the transport conveyor 160along the upper leg 162 and lower leg 164, any manner of track structure174 may be utilized to engage the conveyor 160 along the respectivelegs. In the illustrated embodiment, the conveyor 160 includes rollers142 that engage and roll along the tracks 174, as explained in greaterdetail below.

A heat source 168 is configured adjacent to the lower leg 164 of thetransport conveyor 160 and generates heat effective for sublimating thesource material that plated onto the upper surface 163 of the transportconveyor 160 along the upper leg 162 of the conveyor path. In theillustrated embodiment, the heat source 168 includes a plurality ofheater elements that extend transversely across the width of theconveyor 160 and spaced apart along the lower leg 164 within theconveyor loop such that the upper surface 163 is heated indirectly alongthe lower leg 164 by heating of the underside (inner) surface of theconveyor 160. The pattern, number, spacing, and so forth, of the heaterelements is designed to ensure an even heating of the upper surface 163along the lower leg 164. As the source material sublimates, it diffusesand plates onto the underlying upper surface of the substrate 14 that ismoving along the conveyance path parallel to the lower leg 164. Thediffusion length may be, for example, within a range of about 2 mm toabout 50 mm. The surface of the substrate 14 is at a temperature suchthat the sublimated source material diffuses across the relatively shortdiffusion length and immediately plates on the substrate 14 as a thinfilm layer of the source material. Desirably, there is no interveningstructure between the upper surface of a substrate 14 carried by thesubstrate conveyor 166 and the lower leg 164 of the transport conveyor166 that would inhibit this process by, for example, increasing thediffusion length or presenting other structure on which the sublimatedsource material may condense on.

A cooling unit 178 is disposed in the endless loop path of the transportconveyor 160 after the location where the source material is sublimatedfrom the conveyor and prior to the conveyor 160 returning to its upperleg 162. In the illustrated embodiments, the cooling unit 178 isconfigured adjacent to a sprocket 238 around which the conveyor 160 runsas the conveyor transitions from the lower leg 164 to the upper leg 162.This cooling unit 178 serves to return the upper surface 163 of theconveyor 160 to a temperature that is effective for causing thesublimated source material from the deposition head 110 to plate ontothe surface 163 as the conveyor runs along the upper leg 162. Thecooling unit 178 may be configured as any type of suitable heatexchanger, and may be supplied with a recirculating cooling mediumthrough inlet supply line 180 and outline line 182. The cooling mediummay be, for example, refrigerant, chilled water, gas, or any other typeof suitable medium.

FIG. 2 also depicts thermal shielding 170 disposed to generally isolatethe thermal conditions between the upper leg 162 and lower leg 164. Itshould be appreciated that any manner and configuration of shielding 170may be utilized to effectuate the desired various thermal conditionswithin the apparatus 100 between, for example, the upper leg 162 andlower leg 164 of the transport conveyor 160. Similarly, in theembodiment of FIG. 4 discussed below wherein the substrate conveyor 166is also an endless loop-type conveyor, shielding 170 may be utilizedbetween the upper leg that conveys the substrates adjacent to the lowerleg 164 of the transport conveyor and the lower return leg.

In the embodiment of FIG. 2, the substrate conveyor 166 moves in thesame direction as the transport conveyor 160 along the lower leg 164.The linear speeds of the conveyors 160, 166 may be matched along thelower leg 164 such that relative movement between the conveyors isessentially eliminated during the sublimation and deposition process. Inan alternate embodiment, the substrate conveyor 166 may move in adirection opposite to the transport conveyor 160 along the lower leg164.

It should be appreciated that the type of conveyor configuration usedfor the transport conveyor 160 and substrate conveyor 166 may varywidely within the scope and spirit of the invention. In the embodimentof FIG. 2, the transport conveyor 160 comprises a plurality of slats 230interconnected by link assemblies 240, as discussed in greater detailbelow with respect to FIGS. 5 through 7. The slats 230 each haverespective flat planar outer surfaces that collectively define the uppersurface 163 along the upper leg 162. The link assemblies 240 include therollers 242 that engage the tracks 174 along the upper leg 162 and lowerleg 164, and engage drive cogs on the sprockets 238. In this embodiment,the substrate conveyor 166 is defined by a plurality of spaced apartelongated rollers 176, with at least certain of the rollers 176 beingdriven to convey the substrates 14 through the apparatus 100 at adesired conveyance rate.

FIG. 4 illustrates an embodiment wherein the apparatus 100 is modularand contained within a casing structure 184. This configuration isparticularly suited as a modular component of the system 10 of FIG. 1,for example. The transport conveyor 160 in this embodiment may be asdescribed above with respect to the embodiment of FIG. 2. The substrateconveyor 166 may also be configured as an endless loop conveyor thatmoves around sprockets 238 similar to the transport conveyor 160, andinclude an upper leg 167 that defines the conveyance path for substrates14 through the apparatus 100. As with the transport conveyor 160, thisendless loop conveyor 166 may include a plurality of interconnectedslats 230, with each of the slats 230 having a respective flat planarouter surface that lie in a common horizontal plane in the upper leg 167and define an uninterrupted flat support surface for the substrates 14.The slats 230 may be interconnected by link assemblies 240 at oppositelongitudinal ends of the slats 230. The link assemblies 240 includerollers 242 configured therewith that engage tracks 174 disposed alongthe upper leg 167 of the conveyance path.

FIG. 3 illustrates a particular embodiment of a deposition head 110 thatmay be utilized with the present invention. A receptacle 116 is disposedwithin an interior space and is configured for receipt of a granularsource material (not shown). As mentioned, the granular source materialmay be supplied by a feed device or system 24 (FIG. 1) via a feed tube148 (FIG. 4). The feed tube 148 is connected to a distributor 144disposed in an opening in a top wall 114 of the deposition head 110. Thedistributor 144 includes a plurality of discharge ports 146 that areconfigured to evenly distribute the granular source material into thereceptacle 116. The receptacle 116 has an open top and may include anyconfiguration of internal ribs 120 or other structural elements.

In the illustrated embodiment, at least one thermocouple 122 isoperationally disposed through the top wall 114 of the deposition head110 to monitor temperature within the deposition head 110 adjacent to orin the receptacle 116.

The deposition head 110 also includes side walls and longitudinal endwalls 112. The receptacle 116 has a shape and configuration such thatthe end walls 118 are spaced from the end walls 112 of the head chamber110. Very little clearance exists between the side walls of thereceptacle 116 and side walls of the deposition head 110. With thisconfiguration, sublimated source material will flow out of the open topof the receptacle 116 and downwardly over the end walls 118 as leadingand trailing curtains of vapor over, as depicted by the flow arrows inFIG. 3. Very little of the sublimated source material will flow over theside walls of the receptacle 116.

A heated distribution manifold 124 is disposed below the receptacle 116.This distribution manifold 124 may take on various configurations withinthe scope and spirit of the invention, and serves to indirectly heat thereceptacle 116, as well as to distribute the sublimated source materialthat flows from the receptacle 116. In the illustrated embodiment, theheated distribution manifold 124 has a clam-shell configuration thatincludes an upper shell member 130 and a lower shell member 132. Each ofthe shell members 130, 132 includes recesses therein that definecavities 134 when the shell members are mated together as depicted inFIG. 3. Heater elements 128 are disposed within the cavities 134 andserve to heat the distribution manifold 124 to a degree sufficient forindirectly heating the source material within the receptacle 116 tocause sublimation of the source material. The heater elements 128 may bemade of a material that reacts with the source material vapor and, inthis regard, the shell members 130, 132 also serve to isolate the heaterelements 128 from contact with the source material vapor. The heatgenerated by the distribution manifold 124 is also sufficient to preventthe sublimated source material from plating out onto components of thedeposition head 110. Desirably, the coolest component in the depositionhead 110 is the upper surface 163 of the underlying transport conveyor160 so as to ensure that the sublimated source material plates onto theconveyor 160 and not onto other components of the deposition head 110.

Still referring to FIG. 3, the heated distribution manifold 124 includesa plurality of passages 126 defined therethrough. These passages have ashape and configuration so as to uniformly distribute the sublimatedsource material towards the underlying transport conveyor 160.

In the illustrated embodiment, a distribution plate 152 is disposedbelow the distribution manifold 124 at a defined distance above ahorizontal plane of the upper surface 163 of the underlying conveyor 160(FIG. 2). The distribution plate 152 includes a pattern of passages,such as holes, slits, and the like, therethrough that further distributethe sublimated source material passing through the distribution manifold124 such that the source material vapors are uninterrupted in thetransverse direction. In other words, the pattern of passages are shapedand staggered or otherwise positioned to ensure that the sublimatedsource material is deposited completely over the upper surface 163 ofthe conveyor 160 in the transverse direction so that longitudinalstreaks or stripes of “un-coated” regions on the upper surface 163 areavoided.

As previously mentioned, a significant portion of the sublimated sourcematerial will flow out of the receptacle 116 as leading and trailingcurtains of vapor, as depicted by the arrows flowing over the edges 118in FIG. 3. Although these curtains of vapor will diffuse to some extentin the longitudinal direction prior to passing through the distributionplate 152, it should be appreciated that it is unlikely that a uniformdistribution of the sublimated source material in the longitudinaldirection will be achieved. In other words, more of the sublimatedsource material will be distributed through the longitudinal endsections of the distribution plate 152 as compared to the middle portionof the distribution plate. However, because the transport conveyor 160moves within the vapor deposition apparatus 100 at a constant (non-stop)linear speed, the upper surface 163 of the conveyor 160 will be exposedto the same deposition environment regardless of any non-uniformity ofthe vapor distribution along the longitudinal aspect of the apparatus100. The passages 126 in the distribution manifold 124 and the holes inthe distribution plate 152 ensure a relatively uniform distribution ofthe sublimated source material in the transverse aspect of the vapordeposition apparatus 100. So long as the uniform transverse aspect ofthe vapor is maintained, a relatively uniform thin film layer isdeposited onto the upper surface 163 of the conveyor 160 regardless ofany non-uniformity in the vapor deposition along the longitudinal aspectof the apparatus 100.

As illustrated in the figures, it may be desired to include a debrisshield 150 between the receptacle 116 and the distribution manifold 124.This shield 150 includes holes defined therethrough (which may be largeror smaller than the size of the holes of the distribution plate 152) andprimarily serves to retain any granular or particulate source materialfrom passing through and potentially interfering with operation of themovable components of the distribution manifold 124. In other words, thedebris shield 150 can be configured to act as a breathable screen thatinhibits the passage of particles without substantially interfering withvapors flowing through the shield 150.

Referring to FIG. 3, the apparatus desirably includes transverselyextending seals 154 at each longitudinal end of the deposition head 110.The seals 154 may engage against structure of the underlying transportconveyor 160 assembly, such as a top member 226 that defines an opendeposition area 212, as discussed in greater detail below with respectto FIG. 5. The seals 154 help to maintain the sublimated source materialin the deposition area above the upper surface 163 of the conveyor 160.In other words, the seals 154 prevent the sublimated source materialfrom “leaking out” through the longitudinal ends of the apparatus 100.It should be appreciated that the seals 154 may be defined by anysuitable structure. In the illustrated embodiment, the seals 154 areactually defined by components of the lower shell member 132 of theheated distribution manifold 124.

Any manner of longitudinally extending seal structure 155 may also beconfigured with the deposition head 110 to provide a seal along thelongitudinal sides thereof. Referring to FIG. 3, this seal structure 155may include a longitudinally extending side member that is disposedgenerally as close as reasonably possible to the upper surface of theunderlying upper conveyor surface 163 so as to inhibit outward flow ofthe sublimated source material without frictionally engaging against theconveyor 160.

Referring still to FIG. 3, the illustrated embodiment of the depositionhead 110 includes a movable shutter plate 136 disposed above thedistribution manifold 124. This shutter plate 136 includes a pluralityof passages 138 defined therethrough that align with the passages 126 inthe distribution manifold 124 in a first operational position of theshutter plate 136 as depicted in FIG. 3. As can be readily appreciatedfrom FIG. 3, in this operational position of the shutter plate 136, thesublimated source material is free to flow through the shutter plate 136and through the passages 126 in the distribution manifold 124 forsubsequent distribution through the plate 152. The shutter plate 136 ismovable to a second operational position relative to the upper surfaceof the distribution manifold 124 wherein the passages 138 in the shutterplate 136 are misaligned with the passages 126 in the distributionmanifold 124. In this configuration, the sublimated source material isblocked from passing through the distribution manifold 124, and isessentially contained within the interior volume of the head chamber110. Any suitable actuation mechanism, generally 140, may be configuredfor moving the shutter plate 136 between the first and secondoperational positions. In the illustrated embodiment, the actuationmechanism 140 includes a rod 142 and any manner of suitable linkage thatconnects the rod 142 to the shutter plate 136. The rod 142 is rotated byany manner of mechanism located externally of the deposition head 110.The shutter plate 136 configuration illustrated in FIG. 3 isparticularly beneficial in that the sublimated source material can bequickly and easily contained within the deposition head 110 andprevented from passing through to the deposition area above thetransport conveyor 160. This may be desired, for example, during startup of the system 10 while the concentration of vapors within the headchamber builds to a sufficient degree to start the deposition process.Likewise, during shutdown of the system, it may be desired to maintainthe sublimated source material within the deposition head 110 to preventthe material from condensing on the conveyor 160 or other components ofthe apparatus 100.

FIG. 5 illustrates a conveyor assembly 200 that may incorporate thetransport conveyor 160 in accordance with one embodiment. The assembly200 may include a housing 204 that defines an enclosed interior volume(at least around the sides and top) in which the conveyor 160 iscontained. The conveyor 160 is driven in its endless loop within thehousing 204 around sprockets 238. The housing 204 includes end walls208, side walls, and a top member 210 that defines an open depositionarea 212 through which the upper surface 163 of the conveyor 160 isexposed along the upper leg 162. This open deposition area 212 alignswith the deposition head 110, particularly the distribution plate 88,such that the upper surface 163 of the conveyor 160 is exposed to thedistribution plate 88 in the open deposition area 212.

FIGS. 6 and 7 illustrate components of an endless loop conveyor that maybe used as the transport conveyor 160 and the substrate conveyor 166,for example in the embodiment of FIG. 4. In this embodiment, the slats230 each have a respective flat planar outer surface 232 and atransverse leading edge profile 235 and a transverse trailing edgeprofile 236. The trailing edge profile 236 is inclined or slanted withrespect to vertical. The leading transverse edge profile 235 has achamfered or double-angled profile and cooperates with the trailing edge236 of an adjacent slat 230 so as to define a tortuous non-vertical paththrough the adjacent slats 230 along the upper leg 162 of the conveyor160. This tortuous path inhibits sublimated source material from passingthrough the conveyor slats 230. Referring to FIG. 5, it can be seen thatthe adjacent slats 230 along the upper leg 162 define a flat, planarsurface whereby the outer surfaces 232 of the slats lie in a commonhorizontal plane and define the uninterrupted flat upper surface 163onto which the source material condenses as the conveyor 160 moves alongthe upper leg 162. In the embodiment wherein the conveyor is used as thesubstrate conveyor 166, the flat surface defined by the outer surfaces232 of the slats 230 define a flat support surface for the substrates 14conveyed through the assembly 100. This flat support surface preventsbowing of the glass substrates 14. In addition, the flat conveyorsurface, in combination with the transverse edge profiles of the slats230 discussed above, prevent back side coating of the substrates 14 withsublimated source material.

Referring again to the housing construction 204 depicted in FIG. 5, itcan be seen that the open deposition area 212 in the top wall 210 has atransverse dimension (relative to the transport direction of theconveyor 160) that is less than the transverse length of the underlyingslats 230. In essence, the open deposition area 212 defines a “pictureframe” around a completely flat, planar surface 163 of the conveyor 160in its upper leg 162 of travel. The sublimated source material platesonto the surface 163 within this picture frame, which is thentransferred to the subsequent deposition location adjacent to thesubstrate conveyor along the lower leg 164. The source material istransferred to the upper surface of the substrates 14 in essentially thesame picture frame dimensions. The flat surface 163 defined by the uppersurfaces 232 of the slats 230 is “uninterrupted” in that at no locationwithin the open deposition area 212 can a vertical line be drawn throughthe surface. As described above, even at the transverse edges 235, 236of adjacent slats 230, the transverse edge profiles define anon-vertical tortuous path that inhibits sublimated source material frompassing therethrough.

Referring to FIG. 5, the top wall 210 may include sealing surfaces 226that are engaged by the seals 154 of the deposition head 110, asdiscussed above. This sealing arrangement ensures that the sublimatedsource material that passes through the distribution plate 88 ismaintained in the open deposition area 212 of the top member 210 anddoes not escape at the interface of the conveyor assembly 200 and thedeposition head 110. The open deposition area 212 may be defined so asto have dimensions that define the eventual surface area of the thinfilm layer of source material on the substrates. In other words, thesurface area geometries of the thin film layer on the substrate can becontrolled by defining the dimensions of the open deposition area 212 inthe top member 210.

In a particular embodiment, the conveyor slats 230 are interconnected bylink assemblies 240, as illustrated particularly in FIGS. 6 and 7. Theselink assemblies 240 may take on various configurations. In theillustrated embodiment, the link assemblies 240 include inner and outerlink plates 246, 248. Rollers 242 are contained between the plates 246,248 by respective axles 250. The axles 250 serve to interconnectadjacent inner and outer plates 246, 248 at the respective longitudinalends thereof, and to also rotationally support the rollers 242 betweenthe plates. Each of the inner and outer plates 246, 248 includes a tab252 that extends through a slot in the slats 230. These tabs 252 have anundercut such that after insertion of the tabs 252 through the slots,the plates 246, 248 are shifted relative to the tabs slats 230 to ensurethat the slats 230 cannot be pulled from the plates 246, 248.

Referring to FIG. 5, one end of the axles 250 has an enlarged head thatprevents the axles from being pulled through the plates 246, 248. Theopposite end of the axles 250 protrudes through the outer plates 248. Aclip 256 attaches to the end of the axles 250, and extends between twoaxles. Thus, the clip 256 has a longitudinal length that is essentiallythe same as one of the plates 246, 248, and does not inhibit travel ofthe link assemblies 240 around the sprockets 238.

The present invention also encompasses various process embodiments forvapor deposition of a sublimated source material to form a thin film ona PV module substrate. The various processes may be practiced with thesystem embodiments described above or by any other configuration ofsuitable system components. It should thus be appreciated that theprocess embodiments according to the invention are not limited to thesystem configuration described herein.

In a particular embodiment, the vapor deposition process includessublimating source material in a deposition head and condensing thesublimated source material onto a transfer device, such as a firstconveyor that is disposed below the deposition head. The transfer deviceis moved to a position adjacent to a conveyor that carries substratesthereon. The source material on the transfer device is then sublimatedand condensed (i.e., plates) onto the substrates. The transfer devicemay be a conveyor that is driven in an endless loop path between anupper leg and a lower leg, with the second conveyor moving in aconveyance path adjacent to the lower leg. The first conveyor and thesecond conveyor may move in the same direction along the lower leg ofthe first conveyor. In an alternate embodiment the conveyors may move inopposite directions along the lower leg of the first conveyor. Thesecond conveyor may also move in an endless loop path.

The process may also include heating the first conveyor along the lowerleg to sublimate the source material plated thereon. After the heatingand sublimation, the process may also include cooling the first conveyorprior to the first conveyor moving to the upper leg.

The process includes maintaining a desired diffusion length along thelower leg between the first conveyor and an upper surface of a substratecarried by the second conveyor of between about 2 mm to about 50 mm.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they include structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

1. An apparatus for indirect vapor deposition of a sublimated sourcematerial as a thin film on a photovoltaic module substrate, saidapparatus comprising: a deposition head configured for sublimating asource material supplied thereto; a transfer conveyor disposed belowsaid deposition head onto which the sublimated source material plates,wherein said transport conveyor is movable in an endless loop between anupper leg and a lower leg, said transport conveyor comprises a pluralityof interconnected slats; a substrate conveyor configured to conveysubstrates in a conveyance path through said apparatus; said transferconveyor movable to a position opposite to an upper surface of thesubstrates; and, a heat source configured adjacent to said transferconveyor; wherein source material initially plated onto said transportconveyor is sublimated and transferred to the upper surface ofsubstrates conveyed by said substrate conveyor.
 2. The apparatus as inclaim 1, wherein said transport conveyor comprises an upper surface ontowhich the sublimated source material plates as said transport conveyormoves in said upper leg, said substrate conveyor disposed below saidlower leg, and said heat source configured adjacent said lower leg. 3.The apparatus as in claim 2, wherein said substrate conveyor moves in adirection opposite to said transport conveyor along said lower leg. 4.The apparatus as in claim 2, wherein said substrate conveyor moves inthe same direction as said transport conveyor along said lower leg. 5.The apparatus as in claim 4, said transport conveyor further comprisinga top member, said top member defining an open deposition area in saidupper leg within which the source material plates onto said transportconveyor, said top member further defining a seal surface for saiddeposition head.
 6. The apparatus as in claim 2, wherein each of saidslats has a respective flat planar outer surface and transverse edgeprofiles such that, in said upper leg, said outer surfaces of said slatslie in a common horizontal plane and define an uninterrupted flatdeposition surface presented to said deposition head.
 7. The apparatusas in claim 2, wherein said substrate conveyor is configured directlyopposite said lower leg of said transfer conveyor without interveningstructure between the upper surface of a substrate carried by saidsubstrate conveyor and said lower leg of said transport conveyor.
 8. Theapparatus as in claim 7, wherein a diffusion length for sublimatedsource material from said lower leg of said transport conveyor to theupper surface of the substrates is from about 2 mm to about 50 mm. 9.The apparatus as in claim 1, wherein said substrate conveyor comprises aroller conveyor.
 10. The apparatus as in claim 1, wherein said substrateconveyor comprises an endless loop conveyor having an upper leg thatdefines said conveyance path.
 11. The apparatus as in claim 10, whereinsaid endless loop conveyor comprises a plurality of interconnectedslats, each of said slats having a respective flat planar outer surfaceand transverse edge profiles such that said outer surfaces of said slatslie in a common horizontal plane in said upper leg and define anuninterrupted flat support surface for said substrates.